In general, many process systems contain a mobile flowstream containing a liquefied gas or supercritical fluid under pressure mixed with a liquid. Any dissolved liquid samples or components of interest carried through the process system will also remain dissolved in the flowstream. The principle that simple decompression of the mobile phase flowstream separates the stream into two fractions has great importance with regard to recovering liquid phase out of the flowstream. Removal of the gaseous phase, which can constitutes 50% to 95% of the flowstream during normal operation is critical to successful and efficient recovery of the liquid phase.
In prior collection systems for supercritical chromatography systems, the separation of liquid and gas phases within the process flowstream is enhanced by expanding the flow path prior to entering a collection container, thus eliminating the need to pressurize the collection container. Typically, when the gaseous phase of the flowstream exits at a cold temperature from a flow tube in a room-temperature collection container causing the gas to heat up. When a collection container is filling with liquid phase, the heating and expansion of the colder gaseous phase can cause an effervescence of bubbles at the surface of the liquid in the container, especially when the liquid level approaches to the inlet flow stream discharge. Further, this effect is not limited to only supercritical process flow systems. Any type of process that is designed to recover liquid portions from a high pressure flowstream containing a liquefied gas or supercritical fluid under pressure mixed with a liquid can experience this problem. The effervescence effect can cause an aerosol to form and result in a slight loss of liquid. Even though the loss of liquid is minimal when compared to a much larger volume of liquid collected from the flow stream, some solids dissolved in the liquid phase are potentially carried out of the collection device via the aerosol into a waste gas phase stream. The solids can precipitate from the aerosol and cause build-up and blockages in the outlet line leading from a collection device or a buildup of solids on liquid level sensors in the collection device.
Further, as the collection device fills with liquid, the expanding gaseous phase in the device creates some pressurization of the device before it escapes in an outlet line, for example five to fifteen PSI, even if the pressurization is not necessary for gas/liquid separation. Other parts of the waste flow stream may induce higher backpressure than is necessary for gas/liquid separation. Many collection devices are not manufactured to withstand even moderate pressurization. Thus, for many large size (one liter or more) collection bottles, even moderate amounts of pressure could cause breakage that would spill valuable liquid samples collected from the system.